This relates generally to imaging devices, and more particularly, to image sensors that include row drivers.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate. Column circuitry is coupled to each pixel column for reading out pixel signals from the image pixels. Row control circuitry is coupled to each pixel row for resetting, initiating charge transfer, or selectively activating a particular row of pixels for readout.
Machine-vision and other high-speed imaging applications demand global shutter operation with strict exposure control requirements. Depending on lighting conditions, minimizing the integration time is necessary in order to reduce motion artifacts and motion blur. Image sensors supporting global shutter operation typically include imaging pixels each having a photodiode, an anti-blooming transistor for selectively draining the photodiode, a first charge transfer transistor for selectively coupling the photodiode to a storage gate, a second charge transfer transistor for selectively coupling the storage gate to a floating diffusion region, a reset transistor for selectively resetting the floating diffusion region, and associated readout transistors.
The anti-blooming transistor and the first charge transfer transistor are often much larger devices than the reset and readout transistors. As a result, these bigger devices collectively present a large capacitive loading on the respective row control lines. The row driver circuitry have to drive these row control lines with large loading capacitance, which severely limits the performance of the image sensor.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.